<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
</head>
<body>
<script>
    var a;
    console.log(typeof a);
    a = 1;
    console.log(typeof a);
    a = "123";
    console.log(typeof a);
    a = false;
    console.log(typeof a);

    function t1(a, b, c, d) {
        //关键字写法
        console.log(typeof a);
        console.log(typeof b);
        console.log(typeof c);
        console.log(typeof d);
    }
    t1(1, "2", false);

    console.log(typeof(a));
    console.log(typeof(t1));
</script>
</body>
</html>